The lag between the earliest stages of infection and the ability of the tuberculin skin test to detect infection. The tuberculin skin test depends on what is called a delayed-type hypersensitivity reaction that generally does not develop for 2 to 10 weeks after initial infection.
These additional limitations of the tuberculin skin test need to be recognized in implementing skin testing programs and developing policy recommendations and requirements for community and workplace programs for tuberculosis surveillance. As recommended in the recent Institute of Medicine report on the elimination of tuberculosis in the United States (IOM, 2000) and discussed further in Chapter 7, better screening tests are needed to detect latent tuberculosis infection more quickly and more accurately.
Treatment of latent tuberculosis infection helps reduce the likelihood that the infection, especially recent infection, will progress to active disease. Treatment of latent tuberculosis infection is also a major element in public health strategies for the elimination of tuberculosis in the United States because it reduces the proportion of people who will develop active, transmissible disease (IOM, 2000). Thus, treatment benefits both the infected individual and the broader community, including workplaces. Completion of a recommended treatment regimen is estimated to cut the rate of progression from infection to disease by about 80 to 90 percent (ATS/CDC, 2000b).
The drugs used to treat latent tuberculosis infection are a subset of the drugs used to treat active disease, although specific treatment regimens vary. Because treatment of latent tuberculosis infection is not risk-or inconvenience-free, it is usually aimed at individuals at higher risk of developing active disease including those with recent infection and those with AIDS or other conditions that place them at higher risk of progression.
Selection of a treatment regimen depends on the characteristics of the person being treated, for example, whether the person has HIV infection or whether he or she is at high risk for failing to complete the full course of treatment. Alternative regimens vary in their potential risk, and burdens. Therefore, patients should be carefully advised of the options and their possible consequences. Patient preferences need to be considered in selecting a regimen.